N-type carbon nanotube field effect transistor and method of fabricating the same

ABSTRACT

Provided are an n-type carbon nanotube field effect transistor (CNT FET) and a method of fabricating the n-type CNT FET. The n-type CNT FET may include a substrate; electrodes formed on the substrate and separated from each other; a CNT forrmed on the substrate and electrically connected to the electrodes; a gate oxide layer formed on the CNT; and a gate electrode formed on the gate oxide layer, wherein the gate oxide layer contains electron donor atoms which donate electrons to the CNT such that the CNT may be n-doped by the electron donor atoms.

BACKGROUND OF THE DISCLOSURE

This application claims the benefit of Korean Patent Application No.10-2004-0078544, filed on Oct. 2, 2004, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

1. Field of the Disclosure

Embodiments of the present disclosure relate to a field effecttransistor (FET) having n-doped carbon nanotube (CNT) and a method offabricating the n-type CNT FET, and more particularly, to an n-type CNTFET having n-doped CNT which may be manufactured by adsorbing electrondonor atoms on a CNT layer and a method of fabricating the n-type CNTFET.

2. Description of the Related Art

CNTs have excellent mechanical and chemical properties and may have along length of up to one micrometer with a diameter ranging from severalnanometers to several tens of nanometers. CNTs have excellent electricalconductivity and may be applied to electronic devices. Vigorous researchhas been conducted on the use of CNTs in various devices and they arenow used in electric field emission devices, optical switches in thefield of optical communication, biodevices, etc.

Methods of manufacturing CNTs are well known in the art. Examplesinclude arc discharge, pulsed laser vaporization, chemical vapordeposition, screen printing and spin coating.

To use CNTs in a semiconductor device, such as a complementarymetal-oxide-semiconductor (CMOS) transistor, p-type and n-type MOStransistors are required. In general, CNTs are easily to be hole-doped(p-type doped).

U.S. Patent Application Publication No. 2003-122,133 describes a methodof manufacturing an n-type nanotube using an oxygen or potassium ion asa dopant. However, an oxygen molecule cannot be easily decomposed intooxygen atoms and it is difficult to handle potassium ions.

To overcome these problems, U.S. Pat. No. 6,723,624 suggests anothern-type doping method. In this method, silicon nitride (SiNx) isdeposited on the CNT using plasma-enhanced chemical vapor-phaseddeposition (PECVD), and then heated, thereby manufacturing an n-type(electron-doped) CNT.

SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure may provide a field effecttransistor (FET) having n-doped CNT which may be manufactured by forminga gate oxide layer containing electron donor atoms on a CNT layer, whichmay be a channel region, and a method of fabricating the n-type CNT FET.

According to an aspect of the present disclosure, there may be providedan n-type CNT FET comprising: a substrate; electrodes formed on thesubstrate and separated from each other; a CNT formed on the substrateand electrically connected to the electrodes; a gate oxide layer formedon the CNT; and a gate electrode formed on the gate oxide layer, whereinthe gate oxide layer may contain electron donor atoms which donateelectrons to the CNT such that the CNT may be n-doped by the electrondonor atoms.

The gate oxide layer may be formed by depositing an oxide or a nitridecontaining a group V atom using an atomic layer deposition (ALD)process.

The group V atom may be bismuth.

The oxide may be bismuth titanium silicon oxide (BTSO).

According to another aspect of the present disclosure, there may beprovided an n-type CNT FET comprising: a conductive substrate; a gateoxide layer formed on the conductive substrate; electrodes formed on thegate oxide layer and separated from each other; and a CNT formed on thegate oxide layer and electrically connected to the electrodes; whereinthe gate oxide layer contains electron donor atoms which donateelectrons to the CNT such that the CNT may be n-doped by the electrondonor atoms.

According to still another aspect of the present disclosure, there maybe provided a method of fabricating an n-type CNT FET comprising:forming electrodes separated from each other on a substrate; forming aCNT on the substrate such that the CNT may be electrically connected tothe electrodes; forming a gate oxide layer on the CNT by depositing anoxide or a nitride containing electron donor atoms; forming a gateelectrode on the gate oxide layer, wherein the CNT may be n-doped by theelectron donor atoms.

According to yet another aspect of the present invention, there may beprovided a method of fabricating an n-type CNT FET, comprising: forminga gate oxide layer on a conductive substrate by depositing an oxide or anitride containing electron donor atoms on the substrate; formingelectrodes separated from each other on the gate oxide layer; andforming a CNT on the gate oxide layer such that the CNT may beelectrically connected to the electrodes, wherein the CNT may be n-dopedby the electron donor atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of embodiments of thepresent invention will become more apparent by describing in detailexemplary embodiments thereof with reference to the attached drawings inwhich:

FIG. 1 is a cross-sectional view of an n-type carbon nanotube fieldeffect transistor (CNT FET) according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of an n-type CNT FET according toanother embodiment of the present invention;

FIGS. 3 and 4 are I-V graphs of CNT FETs before and after the depositionof bismuth titanium silicon oxide (BTSO);

FIGS. 5A through 5E are cross-sectional views illustrating a method offabricating an n-type CNT FET according to an embodiment of the presentinvention; and

FIGS. 6A through 6C are cross-sectional views illustrating a method offabricating an n-type CNT FET according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT OF THE DISCLOSURE

Hereinafter, an n-type carbon nanotube field effect transistor (CNT FET)having an n-type CNT and a method of fabricating the n-type CNT FETaccording to embodiments of the disclosure will be described in detailwith reference to the attached drawings.

FIG. 1 is a cross-sectional view of an n-type CNT FET according to anembodiment of the disclosure.

Referring to FIG. 1, an insulating layer 11 may be formed on a substrate10. A CNT 12 may be formed on the insulating layer 11 and electrodes 13and 14 may be formed on both ends of the CNT 12, respectively. Theelectrodes 13 and 14 may function as a drain region and a source region,respectively, and the CNT 12 may function as a channel region.

A gate oxide layer 15 may cover the CNT 12 and a gate electrode 16 maybe formed on the gate oxide layer 15, between the electrodes 13 and 14.

The gate oxide layer 15 may be formed of an oxide or a nitride and mayfunction as an electron donor layer. The gate oxide layer 15 may containa group V atom, such as N, P, As, Sb or Bi. The gate oxide layer 15 maybe composed of bismuth titanium silicon oxide (BTSO) and may be formedusing an atomic layer deposition (ALD) process. When the CNT 22 isdeposited on the BTSO layer, the bismuth may donate electrons to the CNT12, thereby n-doping a surface of the CNT 12. The electronic deviceillustrated in FIG. 1 is a top gate n-type CNT FET.

FIG. 2 is a cross-sectional view of an n-type CNT FET according toanother embodiment of the present disclosure.

Referring to FIG. 2, a gate oxide layer 21 may be formed on a conductivesubstrate 20, for example, a highly doped silicon wafer. A CNT 22 may beformed on the gate oxide layer 21 and electrodes 23 and 24 may be formedbelow both ends of the CNT 22, respectively. The electrodes 23 and 24may function as a drain region and a source region, respectively, andthe CNT 22 may function as a channel region. The conductive substrate 20functions as a gate electrode.

The gate oxide layer 21 may be formed of an oxide or a nitride and mayfunction as an electron donor layer. The gate oxide layer 21 may containa group V atom, such as N, P, As, Sb or Bi. The gate oxide layer 21 maybe composed of BTSO and may be formed using an ALD process. When theBTSO layer is deposited on the CNT 22, the bismuth may donate electronsto the CNT 22, thereby n-doping a surface of the CNT 22. The electronicdevice illustrated in FIG. 2 is a bottom gate n-type CNT FET.

FIGS. 3 and 4 are I-V graphs of CNT FETs before and after the depositionof BTSO, respectively.

Referring to FIG. 3, CNT before deposition of BTSO may be slightlyp-doped. When a voltage V_(ds) is applied to a drain electrode and asource electrode and a gate bias voltage V_(g) is applied in thenegative direction, the transistor may be turned on. Thus, the CNT mayexhibit p-type characteristics.

Referring to FIG. 4, CNT after deposition of BTSO may be n-doped. When avoltage V_(ds) is applied to a drain electrode and a source electrodeand a gate bias voltage V_(g) is applied in the positive direction, thetransistor may be turned on. Thus, the CNT exhibits n-typecharacteristics. Thus, the CNT is n-doped by depositing BSTO on the CNT.

FIGS. 5A through 5E are cross-sectional views illustrating a method offabricating an n-type CNT FET according to an embodiment of the presentdisclosure.

Referring to FIG. 5A, an insulating layer 31, for example, an oxidelayer, may be formed on a substrate 30. When the substrate 30 is made ofa non-conductive material, the insulating layer 31 may be omitted.

Referring to FIG. 5B, a conductive layer may be formed on the insulatinglayer 31 and patterned to form a drain electrode 33 and a sourceelectrode 34, which are separated from each other.

Referring to FIG. 5C, a CNT 32 may be formed on the insulating layer 31such that the CNT 32 is electrically connected to the electrodes 33 and34. The CNT 32 may be grown directly on the insulating layer 31 orformed using a conventional method, such as screen printing, spincoating, etc. This CNT 32 may exhibit p-type characteristics.

Referring to FIG. 5D, a gate oxide layer 35 may be deposited on the CNT32. The gate oxide layer 35 may be formed by depositing BTSO using anALD process at 300° C. Water vapor may be used as an oxygen source. Whenthe BTSO layer is deposited on the CNT 32, electrons from the BTSO layermay be adsorbed by a surface of the CNT 32, and thus, the CNT 32 may ben-doped. Since the gate oxide layer 35 may be used as an electron donorlayer, the n-doping may be easily performed in a simplified process.

Although the gate oxide layer 35 may be formed of an oxide in the abovedescription, the composition of the gate oxide layer 35 need not belimited thereto. The gate oxide layer 35 may contain one of N, P, As, Sband Bi, which are group V atoms.

Referring to FIG. 5E, a gate electrode 36 may be formed on the gateoxide layer 35, between the electrodes 33 and 34. The gate electrode 36may be formed using a pattering process.

FIGS. 6A through 6C are cross-sectional views illustrating a method offabricating an n-type CNT FET according to another embodiment of thedisclosure.

Referring to FIG. 6A, a gate oxide layer 41 may be formed on aconductive substrate 40, such as a highly doped silicon substrate. Thegate oxide layer 41 may be formed by depositing BTSO using an ALDprocess at about 300° C. Water vapor may be used as an oxygen source.

Referring to FIG. 6B, a conductive layer may be formed on the gate oxidelayer 41 and patterned to form a drain electrode 43 and a sourceelectrode 44, which may be separated from each other.

Referring to FIG. 6C, a CNT 42 may be formed on the gate oxide layer 41by direct growth on the gate oxide layer 41 or using a conventionalmethod, such as screen printing, spin coating, etc. Electrons from thegate oxide layer 41 of the BTSO may be adsorbed by a surface of the CNT42, which has p-type characteristics, and thus, the CNT 42 may ben-doped.

In the method of fabricating the n-type CNT FET according to the presentinvention, the CNT may be n-doped using a gate oxide layer which mayfunction as an electron donor layer. Thus, the n-doping may be easilyperformed in a simplified process.

In addition, in the method of fabricating the n-type CNT FET accordingto an embodiment of the present disclosure, conventional p-doped CNT maybe converted to n-doped CNT, and thus, may be applied to a logic devicecomprising a p-type device and an n-type device, etc.

While embodiments of the present disclosure have been particularly shownand described with reference to exemplary embodiments thereof, it willbe understood by those of ordinary skill in the art that various changesin form and details may be made therein without departing from thespirit and scope of the present invention as defined by the followingclaims.

1. An n-type carbon nanotube field effect transistor (CNT FET)comprising: a substrate; electrodes formed on the substrate andseparated from each other; a CNT formed on the substrate andelectrically connected to the electrodes; a gate oxide layer formed onthe CNT; and a gate electrode formed on the gate oxide layer, whereinthe gate oxide layer contains electron donor atoms which donateelectrons to the CNT such that the CNT is n-doped by the electron donoratoms.
 2. The n-type CNT FET of claim 1, wherein the gate oxide layer isformed by depositing an oxide or a nitride containing a group V atomusing an atomic layer deposition (ALD) process.
 3. The n-type CNT FET ofclaim 2, wherein the group V atom is bismuth.
 4. The n-type CNT FET ofclaim 3, wherein the oxide is bismuth titanium silicon oxide (BTSO). 5.An n-type CNT FET comprising: a conductive substrate; a gate oxide layerformed on the conductive substrate; electrodes formed on the gate oxidelayer and separated from each other; and a CNT formed on the gate oxidelayer and electrically connected to the electrodes; wherein the gateoxide layer contains electron donor atoms which donate electrons to theCNT such that the CNT is n-doped by the electron donor atoms.
 6. Then-type CNT FET of claim 5, wherein the gate oxide layer is formed bydepositing an oxide or a nitride containing a group V atom using an ALDprocess.
 7. The n-type CNT FET of claim 6, wherein the group VA atom isbismuth.
 8. The n-type CNT FET of claim 7, wherein the oxide is BTSO. 9.A method of fabricating an n-type CNT FET comprising: forming electrodesseparated from each other on a substrate; forming a CNT on the substratesuch that the CNT is electrically connected to the electrodes; forming agate oxide layer on the CNT by depositing an oxide or a nitridecontaining electron donor atoms; forming a gate electrode on the gateoxide layer, wherein the CNT is n-doped by the electron donor atoms. 10.The method of claim 9, wherein the gate oxide layer is formed bydepositing an oxide or a nitride containing a group V atom using an ALDprocess.
 11. The method of claim 10, wherein the group V atom isbismuth.
 12. The method of claim 11, wherein the oxide is BTSO.
 13. Amethod of fabricating an n-type CNT FET, comprising: forming a gateoxide layer on a conductive substrate by depositing an oxide or anitride containing electron donor atoms on the substrate; formingelectrodes separated from each other on the gate oxide layer; andforming a CNT on the gate oxide layer such that the CNT is electricallyconnected to the electrodes, wherein the CNT is n-doped by the electrondonor atoms.
 14. The method of claim 13, wherein the gate oxide layer isformed by depositing an oxide or a nitride containing a group V atomusing an ALD process.
 15. The method of claim 14, wherein the group Vatom is bismuth.
 16. The method of claim 15, wherein the oxide is BTSO.